1. Field of the Invention
The present invention generally relates to ink jet printhead apparatus interconnectable with an associated drive system from a single side thereof.
2. Description of Related Art
A piezoelectrically actuated ink jet printhead is a relatively small device used to selectively eject tiny ink droplets onto a paper sheet operatively fed through a printer, in which the printhead is incorporated, to thereby form from the ejected ink droplets selected text and/or graphics on the sheet. In one representative configuration thereof, an ink jet printhead has a horizontally spaced parallel array of internal ink-receiving channels. These internal channels are covered at their front ends by a plate member through which a spaced series of small ink discharge orifices are formed. Each channel opens outwardly through a different one of the spaced orifices.
A spaced series of internal piezoelectric sidewall portions of the printhead body separate and laterally bound the channels along their lengths. To eject an ink droplet through a selected one of the discharge orifices, the two printhead sidewall portions that laterally bound the channel associated with the selected orifice are piezoelectrically deflected into the channel and then returned to their normal undeflected positions. The driven inward deflection of the opposite channel wall portions increases the pressure of the ink within the channel sufficiently to initiate the ejection of a small quantity of ink, in droplet form, outwardly through the discharge orifice.
The electrical signals required to create and control the requisite printhead channel sidewall deflections are typically generated by a suitable electronic driver. Due to the large number of very closely spaced ink channels present in even a small ink jet printhead structure, the resulting number of these electrical signals is quite high, while the physical area available at each ink channel for making the necessary printhead/driver connection is quite small. Accordingly, the connection of the printhead to its associated electronic driver has typically presented a significant connectivity design challenge.
One approach to this connectivity problem has been to mount the electronic driver directly on the printhead body with accompanying circuitry to eliminate the need for a large number of interconnects from the printhead structure to the overall ink jet printing system. Most commonly, this was accomplished by providing an elongated lower body portion of which the top side surface of the rear portion thereof provided a surface, commonly referred to as the "back porch", for mounting the aforementioned electronic driver and accompanying circuitry and an area for interconnecting the remainder of the printer electronics with the electronic driver. However, as detailed below, this approach undesirably results in a very substantial increase in the overall cost of the printhead structure.
Another approach to this connectivity problem has been to mount the electronic driver remotely from the printhead and provide the requisite electrical connections from the printhead channel sidewalls to the remotely disposed driver. One method previously proposed for providing this printhead-to-driver interconnect structure has been to form a high density, parallel array of electrically conductive surface traces on the back porch of the printhead body and use a specially designed flexible ribbon connector to form the connection between these high density traces and a much lower density parallel array on a printed circuit board associated with the driver.
In accordance with this method, the flexible connector has formed thereon a high density series of electrically conductive surface traces registrable with the traces on the back porch of the printhead body, a low density series of electrically conductive surface traces registrable with corresponding traces on the driver circuit board, and a trace "fan-out" section interconnecting the high and low density connector traces. In actually forming the printhead-to-driver interconnection, the high and low density trace sections on the flexible connector are respectively soldered (using a pressure/heat reflow process) to the high density trace section on the printhead body and to the low density trace section on the driver circuit board.
Despite this rather straightforward approach to electrically interconnecting the printhead to an associated electronic driver, the use of a flexible ribbon connector in this manner also greatly increases the cost associated with the overall printhead/driver system. Because of the significant pitch transition required in the flexible connector (a representative transition being from about a 3 mil pitch to about a 50 mil pitch), the cost of the specially designed flexible connector can substantially exceed the cost of the printhead structure with which it is used.
Additionally, in all of the aforementioned techniques, the use of the rear portion of the ink jet printhead, whether for mounting a drive system or interconnecting a flexible connector, makes interconnection of the printhead with an ink supply, most commonly using an ink manifold formed in the rear portion of the printhead, increasingly difficult. Passivization processes, in which the interior side surfaces of the channels are coated with an inactive material are equally complicated by the use of the rear portion of the ink jet printhead for mounting or interconnecting a drive system in that the drive system and any interconnections thereto must be kept clean from the material used to passivate the channels. Finally, the requirement of a projecting lower body portion to form the back porch for mounting or interconnection purposes wastes a significant amount of material, thereby adding to the cost of manufacturing such a printhead.
In view of the foregoing it can readily be seen that it would be desirable to provide a ink jet printhead interconnectable with an associated drive system from one side thereof and a method of manufacturing such a printhead. It is accordingly an object of the present invention to provide such a printhead.